Tectonic control on mantle-source helium migration at the southeastern Tibetan Plateau margin

Abstract The geodynamic mechanisms underlying the development of the southeastern margin of the Tibetan Plateau (SETP) remain unclear. Several models of deformation have been proposed and have primarily been assessed by GPS and geophysical data. In recent years, an increasing amount of geochemical data pertaining to geothermal gases in the vicinity of the SETP has been collected. Upon examining and analyzing the He inventory and its spatial variation patterns, we determined that the transportation mode for deep volatiles in the SETP corroborates the existence of crustal flow. Gas samples from the Sichuan basin and the middle section of the Anninghe-Xiaojiang fault system exhibit typical crustal He degassing (RC/RA < 0.1 RA, where RA is atmospheric [air] 3He/4He, and RC is air-corrected 3He/4He), whereas mantle-derived fluids are unequivocally detected in the remainder of the SETP (RC/RA > 0.1 RA). This process involves the lateral movement of crustal flows, which convey mantle noble gas signals from the Tibetan Plateau to the Yangtze craton. The significant mantle signal in the bending section of the Xianshuihe fault system is attributed to the swift migration of mantle fluids through the crust, demonstrating that crustal movement can exert additional impacts on vertical movement of mantle fluids. Our results are supportive of the existence of crustal flow, supporting the hypothesis that the uplift and expansion of the SETP are relevant to the crustal flows. At the same time, our study also emphasizes that the influence of crustal movement on deep fluid migration cannot be ignored.